1. Field of the Invention
The present invention relates to a device having the function of modulating the amplitude, phase or frequency of light waves or switching optical paths.
More particularly, it relates to optical devices in which the modulations are effected with light (control light) thereby to permit high-speed operations. Such improved optical devices include, for example, devices called an optical modulator, an optical switch, an optical bistable device, an optical logic device and an optical memory device. In particular, the present invention concerns optical devices well suited for applications to optical communications and optical information processing systems of which the information processing abilities of high speed and large capacity are required.
2. Description of the Related Art
As an optical device for modulating light, there has heretofore been known, for example, one described in Applied Physics Letters, vol. 45 (1), 1, July, 1984, p. 13 to p. 15 (Miller et al.). As shown in FIG. 1, it is so constructed that incident light 17 is caused to enter a device which is formed of a triple-layer stacked structure of p (11)-, i (13)- and n (12)-types having a multiple quantum well (MQW) 14 made of GaAs/GaAlAs, and that the incident light 17 is modulated under an electric field applied by an external electric signal source 16, thereby to obtain output light 18. With the prior art, the device is electrically driven. This poses the problem that the modulation speed of the device is limited by the product of a load resistance 15 and the capacitance between electrodes (not shown), namely, by a CR time constant. It has been difficult to employ such a device for high-speed modulation.